Damper assemblies are used in vehicle suspension systems to dissipate energy from road forces applied to the vehicle wheels as the vehicle travels over a road. Generally, the damper assemblies control the transfer of forces to the sprung mass of the vehicle. Dampers act between the vehicle wheels and sprung mass to control the energy transfer to the vehicle frame and body while maintaining contact between the tires and the road.
Monotube dampers utilize a single tube, with a piston assembly movable within the tube. The piston assembly is connected to the vehicle body, and the single tube of the damper is coupled to a tire and wheel assembly. A piston-rod of the piston assembly moves within the single tube and a portion of the rod of the piston-rod extends out of the tube. A gas chamber with a floating piston of the piston assembly is housed at an end of the single tube opposite a rod end of the piston-rod. The floating piston separates a gas chamber of the single tube and a fluid-filled chamber of the single tube. The floating piston moves to accommodate the volume displacement caused by the moving piston-rod. The gas chamber is filled with a gaseous fluid and the fluid-filled chamber is filled with a liquid. Some of the gaseous fluid can be stored in the gas chamber being located in a separate container from the single tube, and this gaseous fluid is fluidly connected to the single tube proximal to the end of the single tube opposite the rod end.
Twintube dampers utilize a pair of tube which are positioned concentric to each other. Therefore, an inner tube is nested or surrounded by an outer tube, and these tubes are in fluid communication with each other. Specifically, the inner and outer tubes are concentric to each other. The inner tube is filled with a liquid and the outer tube is partially filled with the liquid and partially filled with a gaseous fluid. Therefore, the outer tube presents a gas chamber. A piston assembly is movable within the inner tube. The piston assembly is connected to the vehicle body, and the twintube of the damper is coupled to a tire and wheel assembly. A piston-rod moves within the inner tube and a portion of the rod of the piston-rod extends out of the tube.
For the monotube, pressurized gas in the gas chamber requires a static pressure level commensurate with a desired damping ability of the damper assembly. Seals within the damper, such as a seal around the moving rod of the piston-rod, is designed in accordance with the static and dynamic range of pressures. A high static pressure level and tight rod seal will contribute to friction against the moving rod.
Some suspension systems are passive, so that pre-load, spring rate, and ride height of the vehicle are nonadjustable, single predetermined values determined by the design of the damper assembly. In some systems, pre-load, spring rate, and ride height are variable, but not all in a controlled manner. Other suspension systems are actively controlled, so that the spring rate or the preload of the vehicle can be varied. One active design utilizes a monotube damper with an external accumulator.